Preparation Of Dendrimer COS/PAMAM And Study On Antibacterial Activity

Chitosan is the second natural polysaccharide resource after cellulose with abundant reserves,wide source and low price.As the derivatives in the deacetylation of chitin,chitosan has many advantages of good biocompatibility,non-toxic,biodegradability and antibacterial activity and so on,which is widely applied to multiple fields such as food,medicine,environmental protection,agriculture etc..However,chitosan,as a kind of antibacterial material,has a lot of shortcomings,like poor water solubility,limited antibacterial ability and excessive dosage.The degradation of chitosan can not only greatly improve the water-solubility,but also enhance its antibacterial activity.The chitooligosaccharide?COS?obtained from the degradation didn't change the chemical structure units,and retained the active groups of chitosan,which could be chemically modified to enhance the antibacterial properties further.This study based on literature review about degradation,modification and antibacterial properties of chitosan.3 generations COS/PAMAM dendrimer bactericide was prepared by two steps:first,chitosan was degraded by the combination of physical and chemical and enzymatic hydrolysis,then the chitooligosaccharide happened Michael addition reaction to graft Methyl acrylate?MA?and Ethylenediamine?EDA?repeatedly by divergent method.According to the test results of the minimum inhibitory concentration?MIC?and minimum bactericidal concentration?MBC?that the amino terminated COS/PAMAM derivatives acted on Escherichia coli,Pseudomonas aeruginosa,Staphylococcus aureus and Bacillus subtilis,the molecule with excellent bactericidal properties was screened to adsorb Cu2+ and Ag+ further,in order to improve antibacterial activity.The main contents are as follows:1.Chitosan was degraded by the method that microwave/ultrasonic/UV assisted H2O2 and non-specific enzymatic hydrolysis,to obtain the Chitooligosaccharide with the viscosity average molecular weight?M??is 4567.34,the number average molecular weight?Mn?is 3231.28,the weight average molecular?Mw?is 6759.10,the degree of deacetylation?DD?is 96.85%.2.Chitooligosaccharide was modified by grafting PAMAM dendrimer.Firstly,the free radical reaction between COS and MA was initiated by CAN?Ce?NH4?2?NO3?6?to synthesize G0.5.The reaction conditions of GO.5 were determined by the single factor experiments and the response surface methodology.The optimum conditions are that the reaction time is 8h,the initiator dosage is 1.65g?1g COS as the reaction substrate?,the molar ratio of COS:MA?g/mL?is 1:8.5,and the temperature is 47.5?.Then,the EDA and MA were grafted repeatedly by Michael addition reaction according to the principle of PAMAM dendrimers.The grafting rates of GO.5,G1.5 and G2.5 were 52.38%,44.37%and 27.48%,respectively.The amino content of G1.0,G2.0 and G3.0 were 89.99%,56.24%and 17.93%,respectively.3.The antimicrobial activity of the amino terminated COS/PAMAM derivatives on E.coli,P.aeruginosa,S.aureus and B.subtilis was evaluated by MIC,MBC,the growth inhibition curve and the sterilization rate curve.The results of activity order was as follows:G2.0>G3.0>G1.0.The antibacterial ability of each molecule on four kinds of tested bacteria showed agreement,which is E.coli>B.subtilis>S.aureus>P.aeruginosa.4.G2.0 was selected to adsorb Cu2+ and Ag+,and the loading capacity was measured 92.6mg/g and 124.2mg/g,respectively.The antimicrobial properties of the complexes were tested.The results showed that the inhibit effect was almost unchanged and the capability to kill bacteria was weakened before and after adsorbing Cu²⁺ and Ag⁺.